ABSTRACT Introduction: The effect of oxygen on the surface of resins at the moment of photopolymerization creates a layer which is susceptible to pigments. The use of glycerin may block this effect. Objective: Determine whether there is a difference in the color stability of nanohybrid composite resin subjected to a coloring agent when glycerin is either applied or not applied. Methods: Sixty resin disks were distributed into Group 1 (without glycerin) and Group 2 (with glycerin). Photopolymerization was performed for 20 s with a Bluephase®N LED lamp. The first color measurement was taken with an Easyshase®V spectrophotometer, recording the values obtained for L* (luminosity), a* (red-green axis) and b* (blue-yellow axis). The second color measurement was taken after immersion of the samples for one month in Coca-Cola®, maintaining them in an incubator at 37ºC. Statistical data analysis was performed with Student's t test to determine the color stability changes occurring in the two groups and compare them. Results: Color stability changes were observed in all the resin samples. Mean distance between initial and final color was ΔE = 6.91 in Group 1 and ΔE = 3.74 in Group 2. A statistically significant difference was found between the two groups analyzed (p < 0.001). Conclusions: Glycerin is an effective substance to block the effect of oxygen on the resin surface, preventing the formation of an oxygen-inhibited layer and raising the color stability of the nanohybrid composite resin.

RESUMEN Introducción: El efecto del oxígeno sobre la superficie de las resinas al momento de la fotopolimerización origina una capa que es susceptible a los pigmentos. El uso de la glicerina puede bloquear este efecto. Objetivo: Determinar si existe diferencia en la estabilidad del color de la resina compuesta nano-híbrida sometida a un agente colorante, al aplicar o no la glicerina. Métodos: 60 discos de resina se dividieron en Grupo 1 (sin glicerina) y Grupo 2 (con glicerina). La fotopolimerización se realizó por 20 s con la lámpara LED Bluephase®N. Se realizó la primera medición del color con el espectrofotómetro Easyshase®V y se registraron los valores arrojados para L* (luminosidad), a* (eje rojo-verde) y b* (eje azul-amarillo). Posterior a la inmersión por 1 mes de las muestras en Coca-Cola®, manteniéndolas en una incubadora a 37 ºC, se realizó la segunda medición del color. Se procesaron los datos estadísticamente con la prueba t de Student para determinar las variaciones en la estabilidad del color de ambos grupos y compararlos entre sí. Resultados: En todos los especímenes del experimento existió alteración en la estabilidad del color de la resina. La media de la distancia entre el color inicial y el color final del Grupo 1 fue de ΔE = 6,91, mientras en el Grupo 2 fue ΔE = 3,74. Se halló diferencia estadísticamente significativa entre ambos grupos analizados (p < 0,001). Conclusiones: La glicerina es una sustancia efectiva para bloquear el efecto del oxígeno en la superficie de la resina y evitar la formación de la capa inhibida de oxígeno, aumentando la estabilidad del color de la resina compuesta nano-híbrida.

ABSTRACT: Objective: Determine the color stability of a monochromatic feldspathic ceramic used in CAD / CAM system subjected to immersion in different staining solutions. Methods and materials: 90 monochromatic feldspathic ceramic discs were divided into 3 groups according to staining solution: distilled water, coffee and tea. Three color samples were taken: on days 0, 14 and 28, with a spectrophotometer. To determine the color difference (ΔE *), the 2nd and 1st measure were subtracted for the 14 days; and the 3rd and 2nd measure for the 28 days. Results: The results were interpreted using the National Standards Department Index (NBS). The sample immersed in distilled water presented values ΔE * 1,424 and ΔE * 1,233; the sample in coffee presented values ΔE * 3,327 and ΔE * 3,901; the sample immersed in tea presented values ΔE * 4,597 and ΔE * 5,201. Significant differences were obtained when comparing the chromatic stability in the three staining solutions at 14 and 28 days (p <0.001). Conclusion: There is a significant difference in the chromatic stability of a monochromatic feldspar ceramic subjected to immersion in different staining solutions. Marked color changes were obtained in the samples immersed in coffee and tea.

RESUMEN: Objetivo: Determinar la estabilidad cromática de una cerámica de feldespato monocromática utilizada en sistema CAD/CAM sometida a inmersión de diferentes soluciones de tinción. Materiales y métodos: 90 discos de cerámica feldespática monocromática, divididos en 3 grupos según solución de tinción: agua destilada, café y té. Se realizaron 3 tomas de color: el día 0, 14 y 28, con un espectrofotómetro. Para determinar la diferencia de color (ΔE*), se restó la 2da y la 1era medida para los 14 días; y la 3era y la 2da medida para los 28 días. Resultados: Los resultados se interpretaron utilizando el Índice del Departamento Nacional de Normas (NBS). La muestra inmersa en agua destilada presentó valores ΔE* 1.424 y ΔE* 1.233; la muestra en café presentó valores ΔE* 3.327 y ΔE* 3.901; la muestra inmersa en té presentó valores ΔE* 4.597 y ΔE* 5.201. Se obtuvieron diferencias significativas al comparar la estabilidad cromática en las tres soluciones de tinción a los 14 y 28 días (p<0.001). Conclusiones: Existe diferencia significativa en la estabilidad cromática de una cerámica de feldespato monocromática sometida a inmersión de diferentes soluciones de tinción. Se obtuvieron cambios de color marcados en las muestras inmersas en café y en té.

In long-term oral rehabilitation treatments, resistance of provisional crowns is a very important factor, especially in cases of an extensive edentulous distal space. The aim of this laboratorial study was to evaluate an acrylic resin cantilever-type prosthesis regarding the flexural strength of its in-balance portion as a function of its extension variation and reinforcement by two types of fibers (glass and polyaramid), considering that literature is not conclusive on this subject. Each specimen was composed by 3 total crowns at its mesial portion, each one attached to an implant component (abutment), while the distal portion (cantilever) had two crowns. Each specimen was constructed by injecting acrylic resin into a two-part silicone matrix placed on a metallic base. In each specimen, the crowns were fabricated with either acrylic resin (control group) or acrylic resin reinforced by glass (Fibrante, Angelus) or polyaramide (Kevlar 49, Du Pont) fibers. Compression load was applied on the cantilever, in a point located 7, 14 or 21 mm from the distal surface of the nearest crown with abutment, to simulate different extensions. The specimen was fixed on the metallic base and the force was applied until fracture in a universal test machine. Each one of the 9 sub-groups was composed by 10 specimens. Flexural strength means (in kgf) for the distances of 7, 14 and 21 mm were, respectively, 28.07, 8.27 and 6.39 for control group, 31.89, 9.18 and 5.16 for Kevlar 49 and 30.90, 9.31 and 6.86 for Fibrante. Data analysis ANOVA showed statistically significant difference (p<0.05) only regarding cantilever extension. Tukey's test detected significantly higher flexural strength for the 7 mm-distance, followed by 14 and 21 mm. Fracture was complete only on specimens of non-reinforced groups.